Hello,
I just replaced the diaphragm in my MPS and tuned it using pbanders pages as a guide.
I am very close to the correct setup for my engine, 95mm nickies, Raby 9550 cam, AA rods, 71mm cw crank, lightened flywheel, 8.2:1 compression, stock 2.0L D-Jet.
I was running a FIC MPS, added 270 ohm resistor to the TS II and uplugged the TS I with 35 psi fuel pressure. 24 mph with this setup.
I am now running the MPS calibrated as a 73 2.0L, kept the 270 ohm resistor and plugged the TS I back in and still 35 psi for the fuel pressure. 27 mph with this setup!
I have a slight problem, at onset of throttle, I get a lot of trailer hitching.
Most noticeable at very low speeds.
Thanks in advance for any advice.
Mike

Just bear in mind....I have not read Brad Anders latest so I may not be up to date on what he wrote...but I have tuned hundreds of D-jet systems and MPS's.

Are you referring to bench testing/setting or dynamic/driving testing and setting?

In general...MPS's cannot be properly adjusted on the workbench with an induction meter.......ever. That process is designed just to get you into a close running ballpark so that you can properly adjust the MPS to YOUR engines characteristics......which with a 9550 (excellent choice).....and higher than stock fuel pressure (you need to back your fuel pressure off).....your car is nowhere near stock.

In fact...bench setting is what the factory did....until about 1973...when you start seeing paint marked MPS's appear in 411/412 and 914 cars with the same letter code and part #. The different paint codes denoted subtle adjustments to the baseline fuel setting of the MPS. They finally got smart. You dont just drop a generic bench set MPS with all the same baselines into every engine and expect excellnt results.

By the way...D-jet injectors are known to be prone to failing to seat at 35 psi and above. Its 33 psi max....and in fact....if you are adjusting your MPS...there is no benefit whatsoever to being above 28-30 psi.

There are two main things that will cause the shuddering (called the bucking sysndrome) on deceleration.

1. Did you correctly record and then readjust...the outer full load stop on your MPS? The outer large slotted aluminum plug....is NOT a PLUG. It is a critical adjustment that governs the increase in acceleration of the steel armature pin....out of the coil assembly in the MPS upon collapse of the aneroid chambers when you open the throttle and vent vacuum to air.

It works like this.....at idle...or on deceleration....your vacuum is at its highest. The chambers inside are swelled to maximum pushing the iron rod into the coil and cutting mixture to its leanest. The copper diaphram is also pulled inward against the inner load stop.

Quick important note: were you critically careful upon replacement of your diaphram...to exactly adjust the inner load stop? The inner load stop is the ring that srrounds the very center adjustent screw for your fuel mixture. It has...if you look carefully....an inside or inverse hex pattern to it. In other words it required a 7-8mm hollow allen wrench to hold this ring still while you turn teh inner mixture screw.
If you were not exactly careful not only to adjust this ring screw properly as per your existing MPS.....and also not careful to keep this ring from turning while adjusting your fuel mixture......you have screwed up.

In fact the bench setting methods only real usefulness is to make damn sure that at maximum vacuum...the inner full load stop is properly set to keep the MPS from over leaning you and causing stalling. You may need to go back to the becnh test...add vacuum and make sure that adjusting this ring screw....does not drive the signature from the coil out of spec.

Back to the outer full load stop.....at your highest vacuum (idle and high speed deceleration with throttle closed) when the copper plate is sucked in against the inner load stop.....it opens a gap between the bearing ring in the center of the copper diaphram....and the bearing ring machined onto the inside of that fat outer aluminum plug.

When you step on the gas....the copper plate will accelerate outward against the stop (the aluminum plug) as air rushes in..... faster than the barometric aneroid chambers can contract. This removes spring load pressure from the aneroid chamber stack on one side...allowing the whole stack to push to that side....temporarily....alloowing the armature to outward from the coil faster than it could have just from the aneroids contracting alone.

In short...it does not allow any EXTRA enrichment.....it allows a faster RATE of enrichment off the line. However...if the outer stop/plug is adjusted to tightly it can reduce enrichment.

If you did not count the turns when removing the outer aluminum plug....you can have too much gap between the plug and the copper plate. This usually results in a flat spot off the line and at gear shifts.

If you screw the plug in too tight......it does not allow the engine to have the extra enrichment off the line. It limits the stroke of the copper diaphram. If its way too tight....it will keep the car from idling. A quick check is to idle the car properly....then screw the plug in until it juuuuust...touches the ring on the copper plate. If you move even 1/10th of a turn too far...it will cause idle to drop and maybe even to stall. So...once you get it there...turn it outward about 3/4 turn. Start there. mark it...drive it...and adjust 1/8th turn at a time until it takes off and idles smoothly.

Then..check and readjust your main fuel pressure. DO NOT use 35 psi of fuel pressure. That is too much.

2. The other issue that causes this "shuddering"......is usually an improperly adjusted TPS sensor. Al of the books...100% of them have incomplete or improper procedures for adjusting the TPS. They tell you how to adjust it....but not how to check to see if the contacts are actually in the right spots on the wiper strips....which only about half are.

Also....the best way to properly adjust TPS is with the TB out of the car and in your hand. You must hold the plate tightly closed. Then stroke full cycle to reset the floating contacts...then check again with the VOM.

Also...about 50% of the TPS built after the mid 70's had too much slack between the poles. it can be adjusted but you need to know it. let me know if you need details.

By the way...from the sound of it...your outer full load stop is too tight and your fuel pressure is too high. Ray

Hello Mr. Greenwood,
Thank you for responding, at this point I am driving the car to test, I used Racer Chris's newly produced diaphragms and his D-Jet tuning tools, a small flat blade screwdriver that fits within a tube that has the correct allen size to fit the outer ring along with a hollow full stop screw that has an allen fitting to make adjustments.
The MPS I am working with is for a 1.7 which my engine was originally, it had a cracked diaphragm.
I did not count the number of turns on the inner or outer plugs, but I am somewhat confident that I adjusted it correctly, as gas millage has gone up and my engine temps have gone down almost 10 degrees.

I have to say that I again pulled the wire on the TS I as my idle seemed to low and the bucking seems to be less noticeable.
I am interested in the correct adjustment of the TPS.
I tried to increase my idle using the adjustment knob on the ECU but it did not change making me think it is not adjusted properly.

Also I could use a bit of help with the TPS, I replaced the board with a new one but I did notice the outer pin on the sweeping contacts seemed to be blunted severely, could be that the blunted pin is contacting two points on the circuit board at the same time.

So here is my plan, first I will decrease the fuel pressure back to 29 lbs. than correctly adjust the TPS and than adjust the MPS.

You are on the right track. Everything sounds close. Do the basic outer stopadjustment....it is good that someone else finally got the idea about the proper tools for adjusting. The hollow key..is key so no worry about that. I did a pictorial and post about2 years ago about adjusting and correcting TPS.....and some of this is in the distributor. Give me a day and ill get it back to you. Ray

What ECU are you using?
What 1.7 MPS are you using for the core rebuild? Early ones had a stop ring in the cover to limit WOT while later covers do not._________________70 Ghia Black convert-9/69 build date-stock w/133k 1600 SP-barn find now with a rebuilt tranny and engine
77 Westy 2.0L w/Ljet, Camper Special engine-95hp and with LSD!
76 Porsche 914 2.1L L20c, 120hp Djet

Hello Bleyseng,
I am using a complete '74 D-Jet, I sourced all the correct parts except the MPS, which I bought as a rebuilt unit from Ecklers and used until I was able to get the Racer Chris parts to rebuild my original MPS.
I also replaced the circuit board in the TPS, I added a new wire harness (Bowlsby).
My original MPS Bosch # 0 280 100 049, VW part # 022 906 051 C except the C has an X through it and a hand written E placed at the end of the number.
This MPS seems identical to the one pictured on pbanders pages (short nose type).
The only other modification I made was to remove the decel valve to richen up the mixture. Also using an Ignitor and Bosch Blue coil.
Thanks,
Mike

You are on the right track. Everything sounds close. Do the basic outer stopadjustment....it is good that someone else finally got the idea about the proper tools for adjusting. The hollow key..is key so no worry about that. I did a pictorial and post about2 years ago about adjusting and correcting TPS.....and some of this is in the distributor. Give me a day and ill get it back to you. Ray

Hello Mr. Greenwood,
I intend to readjust the fuel pressure tomorrow and I would like to adjust the TPS correctly before tackling the MPS.

Regarding the MPS, I am a little confused as to what I should be looking for when doing the "basic outer stop adjustment"?

You are on the right track. Everything sounds close. Do the basic outer stopadjustment....it is good that someone else finally got the idea about the proper tools for adjusting. The hollow key..is key so no worry about that. I did a pictorial and post about2 years ago about adjusting and correcting TPS.....and some of this is in the distributor. Give me a day and ill get it back to you. Ray

Hello Mr. Greenwood,
I intend to readjust the fuel pressure tomorrow and I would like to adjust the TPS correctly before tackling the MPS.

Regarding the MPS, I am a little confused as to what I should be looking for when doing the "basic outer stop adjustment"?

Thanks again,
Mike

Sorry its just been busy at work.

Ok....the aluminum plug for the big slotted screwdriver that is in the back of the MPS...opposite the vacuum line end? That is the adjusting screw.

The INNER end of this big fat aluminum screw....is what the copper plate on the inside of the MPS bears up against for a split second or two when you open the throttle. The fat aluminum screw is the outer stop for the copper diaphragm plate inside the MPS.

To adjust this outer stop properly.....first warm the car up. Adjust valves...make sure idle is a perfect as you can get...and make sure that the throttle is 100% closed....no sticky cables etc.....and NO vacuum leaks at all.

Now.... while the car is idling.....mark that fat aluminum screw with a sharpy pen and start backing it out of the MPS. It should have no effect on the running of the car whatsoever at idle....unless you either already had it screwed in too tight....or you have a vacuum leak.

YOU MUST COUNT EXACTLY HOW MANY FULL AND PARTIAL TURNS IT REQUIRES TO REMOVE THIS PLUG/STOP FROM THE MPS!!!!!

So how do you know you if the diaphragm plate is in the right position to adjust...or have any vacuum leaks and all that?

Well...with the plug now out...look at the copper plate with a flashlight. Rev the engine slightly.....you will see the copper diaphragm plate flex outward for a split second. Get it?

When you are idling and throttle 100% closed....the copper diaphragm plate is pulled inward against its inner stop. When you crack the throttle by any amount....the loss of vacuum causes the copper diaphragm plate to flex outward. The big fat aluminum plug is the stop that keeps the plate from flexing too far.

If when you step on the gas and are observing the copper diaphragm plate ....it does NOT flex outward.....it is because you are leaking vacuum somewhere and the plate is already flexed outward. get that fixed first.

Now.....with the engine idling and plate properly vacuumed inward......you screw the big fat aluminum plug back in...until it Just touches the copper plate. Just meeting it exactly...will cause no change to running. Pushing the copper plate even .001" inward.... however...will cause the car to stumble. Get it?

You just want to screw the aluminum plug inward until it meets the copper diaphragm plate WHILE IT IS UNDER VACUUM AT IDLE...ONLY!!!!!!

Then back the big fat aluminum plug out 1/2 turn to start with. Drive it around the block.
If it stumbles off the line and appears lean and pops...no sooty smoke.....the fat aluminum plug needs to be screwed OUT some more....starting about 1/8th of a turn at a time...until this "lean" off the line condition is gone.

You will virtually never be too rich at 1/2 turn outward. Typically right around 3/4 final turns outward will get it.

Understand that the copper diaphragm plate acts just like the accelerator pump on a carb....or vacuum advance on the distributor. It is designed as a rate of enrichment multiplier. If the stop plug is screwed in too tight...its too lean off the line and when shifting. Too far out and its too rich and bogs down. Either way you lose power. Very critical adjustment for smooth D-jet. Ray

Hello Mr. Greenwood,
I think I understand, but I first need to get the TPS dialed in before I start to tune the MPS.
So far the only adjustment procedure I have found is on the Pelican board, which is what I used previously.
I can not increase the idle speed using the "pot" on the ECU, which I believe is caused by an out of adjustment TPS and I am very interested in adjustment of the "rocker contacts" within the TPS.
Thank you again for your help.
Mike

Hello Mr. Greenwood,
I think I understand, but I first need to get the TPS dialed in before I start to tune the MPS.
So far the only adjustment procedure I have found is on the Pelican board, which is what I used previously.
I can not increase the idle speed using the "pot" on the ECU, which I believe is caused by an out of adjustment TPS and I am very interested in adjustment of the "rocker contacts" within the TPS.
Thank you again for your help.
Mike

In general.....idle mixture and the TPS have nothing to do with each other. the exception to this rule.....is if the TPS is being held slightly open by a throttle cable being too tight or.....if as you think it is out of adjustment enough that the forked floating connector inside is in the forward position (enrichment stroke)....then it will bypass/circumvent the idle mixture tuning knob on the ECU.
But....you are really probably nowhere near where you need to be to even be using that knob.

That knob.....really is just a potentiometer that adds ballast to one part of the ECU. Its effect is very similar in actual fuel volume to simply adding ballast to either the CHT or intake air temperature sensor. I am going off memory but I think Brad Anders or someone noted that it gives roughly 10% +/-. It has roughly 25 clicks. If you look closely at it.....you will see an indention in the plastic shield ring around the potentiometer knob that denotes center. That is "0". Turning clockwise adds fuel and turning counterclockwise subtracts fuel.

Just like the other two sensors....this adjustment would add enrichment across the board...but once the TPS moves out of the idle/park position....this potentiometer knobs "ballast"...is simply bypassed.

P.S. I found my file with my TPS instruction with detailed photographs. I originally made a word document of it with omported pictures. Its about 10.5mb. Let me revamp it today. It was originally done for some type 3 people.....but it is the same.
Its an 021 TVS....but the guts of the 018, 019 and 021 are 100% identical down to the circuit board #. Four and five wire makes no difference. Adjustment is the same.

Its not that all of the books give improper incomplete adjustment directions.....its just that there was some large variation in internal tolerance in early to mid 80's replacment parts. The books do not show you what to inspect for after doing the standard adjustment....therefore most will still be out fo adjustment even if they perform the adjustmentcorrectly...unless you know what to look for.

Also some of the later TVS actually had so much slop in teh floating enrichment/shut-off contact as be be physically defective and cause the "bucking syndrome" from day 1. Its easily fixable...but you need to know about it.

Hello Ray,
Thank you for searching for the TVS adjustment document.
Just to note that I am using the 914 2.0L D-Jet which has the 0 280 120 032 switch.
Mike

The switches are really all the same. Very few differences. One with cut off...one without, one with a few more switch pads....very small differences. They all adjust the same (late models).

I forgot to mention The MPS you are using has the same part # variations and similarities. Your original part:
Bosch # 0 280 100 049, VW part # 022 906 051 C except the C has an X through it and a hand written E

The '049 model....the C model.....and the E-model...are all 100% identical parts. There are tuning differences, differences (minor) in build over time....but the largest difference is simply calibration. The "E" is used in VW 412 with 1.7L. The "C" model had some variations like a different spring length but I have found it in both short and long. There were some 411's (late) that this was found in.

The real difference that I have found between the 049 and the "E" series........and knowing that the 049 was used and adjusted to a larger engine like the 2.0L.......is that inside the MPS, the thin spacer ring, that normally goes between the inner stop plate (the one with the keyhole slot in it) and copper diaphragm plate....is reversed.
I am going off memory here....but I believe that on the 049 this spacer ring is between the copper plate and the thin gasket and the back cover of the MPS. This would give the 2.0L MPS about .010" more outward enrichment throw on the copper plate.

Other than these tuning differences....these parts are largely the same. One can be tuned to fit another.
Ray

I did a google search but still could not find any expanded TVS adjustment procedure. Have you had any luck finding the document?
Thanks again,
Mike

I found the document.....I just need to tighten it up a bit (take out the type 3 centric parts and leave in the type 4 parts to avoid confusion) and re-size the pictures. I am on the road right now. I get back tomorrow night. I may have some time to clean it up tonight. Ray

Hello Ray,
I swopped my TVS for a "stock" unit (original circuit board) the best one I had, I got the idle to respond to the ECU adjustment control, replaced the wire to the intake air thermo-sensor.
I had to turn the ECU adjustment knob 4 clicks from the full rich stop to get a good idle.
I started adjusting the MPS full load stop screw. At this point I believe the "bucking" feels better, I have backed the full load stop screw out about 3/4 turn but I can feel a bit of a "stumble or rumble" at cruising speeds, more a feeling than anything I can say is happening.
Thanks again for your help.
Mike

Well the car is turning between Jekyll and Hyde, cold to 180* oil temp it runs fine, easy on bucking, if any and good acceleration.

185* and up to 210* bucks in slow traffic and pings on hard acceleration. Also not shedding the heat as well, along with the sort of rumble at slow cruising speeds.

Gas mileage has gone back up to 27.

My feeling is the engine is leaning out as it gets warm.

If it is lean than pbanders MPS page says to turn the inner stop screw counter-clockwise increasing the pulse width for both partial and full throttle which will enrich the mixture across the board and I assume I need to readjust to outer stop screw?

I should have the TVS tuning guide up tomorrow night. I am stuck in a hotel this evening so I will get a chance to finish it.

Also another major source of bucking....if you still have any.....is the PCV valve if you have one.

This valve is under the rubber elbow in the oil breather box that connects to the 12mm line to the plenum. It is held in with a nylon ring nut from the outside. Some 914's and most 411/412 had them. The issue is that the valve is a spring loaded flap valve. It opens from a COMBINATION of case pressure and vacuum. This means that the ECU has no control over when and what it dumps.

This would not be a huge problem except that the nipple on the plenum that connects to this dumps in right by the MPS nipple. So....if you are borderline rich or lean at any time...when the PCV pops open it affects the MPS at low throttle settings.

Many of us have found much smoother tuning by puncturing the plastic disc inside of the PCV valve...effectively getting rid of it....and instead installing a fixed 3-4mm restriction inside of the 12mm line to the plenum.

this provides all the PCV you will need....and is also manageable with a fine tweak to the idle and MPS. Ray